1. Field of the Invention
The present invention relates to novel silico-titanate compositions of matter, and methods of making and using such compositions.
2. Background Art
Synthesis of molecular sieves and zeolite-type materials are known to the prior art. The crystalline structure of such materials permits cation or anion exchange (or both) as well as water molecule exchange. Further, such materials not only separate molecules of different size, but are capable of segregating molecules of the same size but of different electrical charge.
Among other uses for molecular sieves, or zeolite-type materials, are as xe2x80x9ccarriersxe2x80x9d for certain volatile catalysts, facilitating chemical reactions. The catalysts are trapped and thereby retained in the zeolite molecular structure during the chemical process. Channelized zeolite-type materials resembling tectosilicates, however, are not the only structures that can effect ion exchange. Several phyllosilicates of clay-like materials, for example, montmorillonite (smectite) and vermiculite, readily exchange cations between the tetrahedral layers.
Syntheses of silicon titanate zeolite-type materials is known to the art. U.S. Pat. No. 3,329,481 to Young, entitled Crystalline Titano-Silicate Zeolites, discloses several Group IV-B metallo-silicate zeolites wherein the metal may be a monovalent or bivalent metal, as well as ammonium or hydrogen.
U.S. Pat. No. 4,938,939, to Kuznicki entitled, Preparation of Small-Pored Crystalline Titanium Molecular Sieve Zeolites, discloses a process of producing crystalline titanium zeolite-type compositions having a pore size of 3-5 Angstroms.
U.S. Pat. No. 4,853,202, also to Kuznicki, entitled Large-Pored Crystalline Titanium Molecular Sieve Zeolites, discloses methods of making crystalline titanium molecular sieve compositions having a pore size of about 8 Angstroms.
xe2x80x9cThe OD Structure of Zoritexe2x80x9d Sandomirskii et al., Sov. Phys. Crystallvgr., 24(6), November-December 1979, discloses the crystallographic structure of a naturally occurring alkaline titanosilicate found in Siberia.
U.S. Pat. No. 5,015,453 to Chapman entitled Crystalline Group IVA, Metal-Containing Molecular Sieve Compositions, discloses titanium-silicates, phosphates and phosphosilicates which are three-dimensional microporous crystalline structures.
xe2x80x9cThe Crystal Structure of a New Natural Sodium Titanosilicate,xe2x80x9d by E.V. Sokolova et al., Sov. Phys. Dokl., 34(7), 583-585, July 1989, describes a naturally occurring material, sitinakite, found in the former Soviet Union having an empirical chemical formula of (Na2.251K0.693Ca0.0004Sr0.062Ba0.026Ce0.004)xcexa33.04xc3x97(Ti3.56Nb0.195Fe0.014Zr0.006)xcexa34.03Si1.928O13(O0.45H0.955)xcexa31.00xc3x973.7 H2O which, as an idealized formula, comprises Na2(H2O)2[(Ti4O5(OH)(SiO4)2]K(H2O)1.7. Within this material specimens having higher Nb impurity contents are speculated to have an orthorhombic symmetry.
The present invention relates to silico-titanate compositions (TAMs), structures of these compositions, methods of making these compositions, and methods of using these compositions. The silico-titanate compositions of the present invention (hereafter referred to as xe2x80x9cTAMxe2x80x9d compositions) reside within the range of the general formula and have a mole ratio of:
ySi:aTi;
wherein y comprises a coefficient of between 0.01 and 1.7 and preferably less than 1 and a=1.0.
The TAM composition may further comprise a metal dopant (MD) having the general formula zMD to provide the general empirical formula zMD:ySi:aTi, wherein z is a coefficient having a range of approximately 0.0 to 1.0 and y and a have values as defined above. Useful metal dopants include Group III elements, Group V elements, Group IV elements, Group VIII elements, Group I elements, and compounds thereof, particularly niobium, antimony, vanadium, copper, manganese, iron, phosphorus, tantalum and the like.
The composition may further comprise a cation (M), which are at least in part ion-exchangeable, having the general formula xM, in which event the empirical chemical formula is xM:zMD:ySi:aTi, wherein x is a coefficient having a range of approximately 0.0 to 2.0 and, a, y and z have the values set forth above. Useful cations include Group I elements, Group II elements, hydrogen, ammonium cations and alkylammonium cations. The composition may further comprise elements or compounds such as palladium, platinum, rhodium, molybdenum, nickel and sulfur.
The TAM compositions assume different crystalline structures which are dependent upon the atomic elements comprising the TAM composition and, with respect to a given set of atomic elements the atomic ratios existing therebetween. For example, the existence or not of a Group I or II cation (M) constituent distinguishes TAM-3 (no Group I or II cation constituent) from TAM-1, 2, 5, 7 and 8. Wherein a TAM composition contains a cation (M) constituent, the nature of that cation distinguishes TAM-8 (cation is K) from TAM 1, 2, 5 and 7 (cation is Na). Within a line of TAM compositions having an identical cation (M) content, such as Na in the case of TAM-1, 2, 5 and 7, distinctions in the crystalline structures thereof appear in relationship to the atomic ratios of Si:Ti and M(xe2x95x90Na):Si such that at Si:Tixe2x89xa71.0 and M:Si: less than 1.0 the TAM compositions exhibit as a primary x-ray diffraction line one at 2xcex8 less than 11.00 (TAM-1 and 2) whereas at Si:Ti less than 1.0 and M:Si greater than 1.0 the TAM compositions exhibit as a primary x-ray diffraction line one at 2xcex8 greater than 9.
The present invention further comprises a method of making silico-titanate compositions and products thereof, the method comprising the steps of:
a) providing a reaction mixture containing a titanium source and a silicon source; and
(b) allowing the resulting mixture to react to form the silico-titanate compositions discussed above.
The titanium source is provided from titanium alkoxides, titanium halogens, titanium oxides, and the like. The silicon source is provided from silicon alkoxides (such as tetraethyl orthosilicate), colloidal silica, silicon oxides, sodium silicates and the like. The reactor charge mole ratio of Si to Ti is between 0.01 to 1.7.
The present invention also relates to the use of the TAM compositions as well as other crystalline titanosilicates, such as sitinakite, as ion-exchange materials; e.g., for sequestering radioactive cations from aqueous media as ion-exchange thin film supports; in a catalytic reaction or as catalytic supports, for fluid chemical and biochemical selectivity, such as in treating radioactive waste streams and detection of trace metals; sensors to sense the presence of target chemicals and biochemicals; and in a wide variety of processes, including ion exchange hydrotreating, dehydrogenating, oxidation, epoxidation, reduction, photochemical processes, electrochemical processes, hydrocracking, cracking, hydrogenating and the like.
The method of using the TAM compositions of the invention is particularly useful for chemical or biochemical reactions or removing radioactive matter and trace metals from a fluid stream. This method comprises the steps of:
a) providing the silico-titanate composition discussed above, to the fluid stream; and
b) permitting the radioactive matter or trace metal in the fluid stream to bind to the silico-titanate composition. Binding is accomplished through ion exchange, adsorption, absorption, size selectivity, and the like. This method is particularly useful for removing radioisotopes from waste streams, including cesium, strontium, plutonium, cobalt, iodine, technetium, rhenium, ruthenium, nickel, cerium, uranium, neptunium, americium, lanthanides, actinides, and the like.
Doped silico-titanate compositions are preferable for some applications, including the removal of radioisotopes and trace metals from fluid streams. The preferred dopants are from Group III elements, Group V elements, Group IV elements, Group VIII elements, Group I elements, and compounds thereof, such as niobium, antimony, vanadium, copper, manganese, iron, phosphorus, tantalum, and the like.
The compositions of the present invention have unique shapes, not present in prior silico-titanate compositions. These shapes include elongated strands, parallelepipeds having approximately 90 degree angles, cuboids, ellipsoids, spheres, a collection of elongated strands in spheres, and internal ribbed structures bound substantially by silicon compounds.
The new silico-titanate compositions provide for more efficiently segregating radioactive elements or trace metals from waste streams; are serviceable as catalyst supports or in catalytic reactions; and provide new molecular sieve compositions which are relatively unaffected by changes in pH.
An advantage of the invention is the many methods available for synthesis of the new compositions; is the relative ease of doping the new compositions; and
the use of the new composition as catalysts or as precursors of catalysts.
Additional advantages and novel features of the invention are set forth in the description which follows and will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention.